Problem: Simplify the following expression. $ (5 + (4 - 7 \times 1)) \times 9 $
Explanation: $ = (5 + (4 - 7)) \times 9 $ $ = (5 + (-3)) \times 9 $ $ = (5 - 3) \times 9 $ $ = (2) \times 9 $ $ = 2 \times 9 $ $ = 18 $